This invention concerns door closers of the kind comprising an actuator assembly intended for concealed fitting within the thickness of a door, and an anchor member for fixing to a door frame, and in which an operating member is coupled to said anchor member and is movable within the actuator assembly under the action of driving means, usually comprising one or more mechanical springs, and under the control of a fluid-filled damper (usually uni-directionally operative) which serves to regulate the rate of movement of the door in the direction of closure without significantly restricting the rate of movement of the door in the direction of opening.
It is desirable for the action of any damper in such a door closer to be adjustable so as to enable the rate of closure to be set to fall within a chosen range despite variations in the weight and other parameters of different doors with which the closer may be used, and for the closer to provide an augmented closing force as the door reaches its closed position in order to overcome resistance from any latch fitted to the door. It is also desirable, and often necessary, from a product performance viewpoint, that the arrangement employed to provide such an augmented closing force is able to operate smoothly over a very large number of repeated uses.